Nonspecific interstitial pneumonia (NSIP) has been proposed as a histologic subtype of idiopathic interstitial pneumonia with lung biopsy findings that are inconsistent with those of other idiopathic interstitial pneumonias. NSIP has a broad spectrum of histologic findings and a variable prognosis. The aim of this study was to determine whether it would be preferable to subdivide NSIP into cellular and fibrosing patterns. We classified lung biopsies from 101 patients with idiopathic interstitial lung disease as having histologic patterns of desquamative interstitial pneumonia (DIP), usual interstitial pneumonia (UIP), or cellular or fibrosing NSIP. Survival analysis was performed by the Kaplan-Meier method. Due to histologic, clinical and survival similarities, the cases of idiopathic NSIP with lung biopsies showing fibrosing as well as fibrosing and cellular patterns were combined into a single group of NSIP, fibrosing pattern. Of the 101 patients, 16 (9 females, 7 males) had idiopathic DIP, 56 (17 females, 39 males) had idiopathic UIP, 22 (7 females, 15 males) had idiopathic NSIP, fibrosing pattern and 7 (2 females, 5 males) had idiopathic NSIP, cellular pattern. The patients had mean ages of 42, 51, 50, and 39 years, respectively. Patients with idiopathic NSIP, cellular pattern had a better 5 and 10-year survival than those with idiopathic NSIP, fibrosing pattern (100% vs 90% and 100% vs 35%, respectively, p=0.027). Survival of patients with idiopathic UIP was worse than that of patients with idiopathic NSIP, fibrosing pattern (p=0.014). The difference, however, was more evident at 5 years (43% vs 90%) than at 10 years (15% vs 35%). The 5- and 10-year survival of patients with idiopathic NSIP, cellular pattern and DIP was 100%, which was significantly better that that of patients with idiopathic UIP (P<0.0001). Based on these data NSIP should be separated into cellular and fibrosing patterns, since these histologic patterns are associated with different clinical characteristics and prognoses.